1. Field of the Invention
The present invention relates to a recording-head element substrate, a recording head, and the control circuit configuration of a recording apparatus having the recording head mounted thereon, and more particularly, it relates to the temperature-adjusting control configuration of the recording head.
2. Description of the Related Art
As an information output apparatus of a personal computer, a facsimile machine, or the like, a variety of inkjet recording apparatuses discharging ink through discharge ports arranged so as to correspond to recording elements are known. Of these recording apparatuses, a recording apparatus heating and then discharging ink has electrothermal conversion elements generating energy for discharging ink, incorporated therein so as to serve as recording elements (electrothermal converters), thereby achieving a high-density and high-speed recording performance and being widely available as a low-price color printer or the like.
In a known inkjet recording head, a plurality of recording elements are arranged in a single row or plurality of rows. In the recording head, control wiring terminals are arranged so as to drive a single block of N pieces of recording elements at the same time, an arbitrary recording operation is performed onto a recording material (recording medium) such as a sheet of paper by energizing the recording elements during the period of making the terminals active.
By mounting several or several tens of pieces of driving integrated circuits capable of concurrently driving the recording elements in a unit of a block on the common element substrate, image information can be aligned so as to correspond to each recording element.
The performance of the recording head has drastically improved due to its development for higher definition. An increase in the recording speed of the recording head has been achieved by increasing the number of recording elements or by increasing the number of recording elements that are driven concurrently. The performance of the recording element has been also advanced, resulting in discharging an ink droplet having an amount of several pico litters (10−6 m3) on a pulse having a width of about 1 micro seconds. This performance is achieved with a functional element (such as a MOS-FET driver) capable of switching large electric current at high speed. While the size of the functional element has been reduced year after year, reduction in the size of an inkjet-recording-head element substrate having multiple channels has been advanced.
In recent years, needs for the inkjet-recording-head element substrate having multiple channels have increased mainly for use in a small-sized color inkjet recording head, because a device component forming a color image at low cost is essential for the structure of a currently manufactured product. Several techniques for arranging ink channels for a plurality of colors on the common element substrate are known. For example, with a known technique, the recording elements are arranged in a single row, and the ink channels for discharging mutually different color ink are separated from each other so as to prevent a color mixture of the ink. With another known technique, a single row of the recording elements is allotted to each of a plurality of the ink channels. In addition, another technique arranging recording-element-rows on both sides of each of the plurality of ink channels has been achieved. These techniques are inevitable for achieving a high-speed and high-resolution printing operation, and reducing the sizes of these components is a development issue from now on.
A multiple of types of inkjet recording heads have been developed so as to meet the requirements of the performances of the main bodies of printers having the respective recording heads mounted thereon, and control circuits of the recording heads become complicated. In order to make high-speed and high-resolution inkjet recording heads including these circuits and having a multiple of ink channels, optimization of each control circuit needed for the recording head is an issue of the inkjet-recording-head element substrate.
In addition, controlling drive of the recording head in response to a consumed amount of a recording agent such as ink accommodated in a cartridge and the number of consumed cartridges is often required. Also, controlling the recording head according to a color and a viscosity of ink, a date of manufacture, use application, and the like is often required.
In order to meet the above-described requirements for the inkjet recording head, a known inkjet recording head has devices disposed therein, respectively for detecting its temperature and arbitrarily changing its drive method with an external signal. Also, with a proposed record-controlling method, in order to achieve a high-function, high definition, and low-cost recording apparatus, the recording head includes a device for detecting a difference in the inkjet recording heads due to its manufacturing dispersion.
In a recording apparatus including the inkjet recording head as described above, always discharging a constant amount of ink and landing it onto a recording medium are essential for achieving a higher recording speed and a higher recording density. To this end, controlling the recording elements in the recording head so as to always perform a constant discharge characteristic is needed. For example, a fall of the environmental temperature of the recording apparatus causes a fall of the temperature of ink in the recording head. Therefore, although depending on a property of ink, the recording apparatus sometimes does not perform its original discharge characteristic in the room temperature surroundings.
Hence, even at the time of a low temperature, the temperature of ink is hitherto adjusted up to around a room temperature, for example, by attaching heating devices to the inkjet recording head or building them in the element substrate of the same. Sensors or the like for detecting the temperature are also placed on the inkjet recording head. At the same time, an amount of a discharge ink becomes smaller in recent years, down to several to several tens pico litters (10−6 m3), whereby the discharge characteristic of the recording head tends to be affected by dispersion in temperatures on the inkjet-recording-head element substrate. In such a situation, in order to stably control the temperature of ink, it is necessary to carefully determine the numbers and the locations of the heating devices and the temperature sensors.
In view of these problems, U.S. Pat. No. 5,880,753 proposes a system in which a plurality of head-temperature-adjusting heating devices are arranged on the inkjet recording head so as to individually control ink droplets depending on their temperatures. In this case, the plurality of heating devices is controlled by an external recording apparatus via a plurality of exclusive terminals individually extending from the inkjet recording head. With this arrangement, the number of terminals corresponding to the numbers of the heating devices and the temperature sensors increases. Also, U.S. Pat. No. 6,234,599 proposes the structure of the inkjet recording head, in which the heating devices, each making a pair with the corresponding one of the temperature sensors, are arranged on the inkjet-recording-head element substrate. With this arrangement, the temperature adjusting control at a position as close as possible to the corresponding temperature sensor is achieved. Unfortunately, this arrangement causes an increase in the number of terminals in the same manner as in the foregoing patent document, thereby preventing configuration of a low cost inkjet recording head because the number of terminals of the inkjet recording head increases.
U.S. Pat. No. 6,357,863 discloses the structure of the inkjet recording head, in which, by arranging a plurality of heating devices in parallel to the row of the ink discharge elements, and gradually changing the area of the heating devices from the end to the center of the element substrate, the overall inkjet recording head is uniformly heated. This is an important control from the viewpoint of raising the temperatures of the inkjet recording head and ink up to around a room temperature in a short time when a recording operation is carried out under low temperature circumstances.
With the inkjet recording head in the recent years, due to miniaturization of the droplet of ink as described above, even a fine temperature change affects a discharge characteristic of ink. Not only preheat performed prior to a recording operation by a small number, i.e., one or two, of heating elements, but also controlling the temperature of the recording elements in a unit of block are needed. Hence, while pluralities of the heating devices and the temperature sensors as disclosed in the foregoing patent documents can be arranged in a unit of block, the structure of individually controlling these devices and sensors from outside does not allow a problem of an increase in the number of terminals of the inkjet recording head to be avoided.
The number of recording elements disposed in the inkjet recording head tends to increase, and also, the arrangement density thereof tends to become higher. Hence, the number of blocks for the foregoing time-division drive increases. As a result, an embodiment of the temperature control for every block of the recording elements is accompanied by an additional increase in the number of terminals of the recording elements. Also, since the complicated circuit configuration for controlling the recording elements increases the size of the control circuit on the element substrate of the inkjet recording head, the occupied area of the control circuit increases. For example, in the case of a color inkjet recording head including at least 256 pieces of recording elements, three kinds of ink of cyan, yellow, and magenta colors, a minimum combination for achieving a color image, are prepared. This structure makes the size of the control circuit for individually turning on/off heaters (electrothermal converters) serving as these recording elements large and the occupied area on the element substrate, of even only control wiring lines of the circuit, is also large. When the recording element rows are arranged on both sides of a ink supply port, the control wiring lines simply require a double wide area with the known technique, and many problems including the number and arrangement places of outgoing lines of the terminals of the heating devices remain, thereby causing an obstacle against manufacturing a color inkjet recording apparatus at low cost.